Engine control approaches that vary the effective displacement of an engine by sometimes skipping the firing of certain cylinders are often referred to as “skip fire” engine control. In general, skip fire engine control is understood to offer a number of potential advantages, including the potential of significantly improved fuel economy in many applications. Although the concept of skip fire engine control has been around for many years, and its benefits are understood, skip fire engine control has not yet achieved significant commercial success in part due to the challenges it presents. In many applications such as automotive applications, one of the most significant challenges presented by skip fire engine control is vibration control. In general, a stereotype associated with skip fire engine control is that skip fire operation of an engine will make the engine run significantly rougher than conventional operation. The inability to satisfactorily address vibration concerns is believed to be one of the primary obstacles that has prevented widespread adoption of skip fire.
Co-assigned U.S. Pat. Nos. 7,577,511, 7,849,835, 7,886,715, 7,954,474, the referenced priority applications, and others describe a new class of engine controllers that make it practical to operate a wide variety of internal combustion engines in a skip fire operational mode. Although the described controllers work well, there are continuing efforts to further improve their performance and to further reduce the vibration of engines operating under their control. The present application expands upon the earlier patents and describes additional control features and enhancements that may further improve performance in a variety of applications.